Perforation of sheet material by electrical discharges



July 3, 1945. l. H. wlLsL-:Y Erm.

PERFORATION OF SHEET MATERIAL BY ELECTRICAL DISCHARGES Filed Aug. 9, 1941 @slanted4 July 3, 1945 PERFORATION F SHEET MATERIAL BY ELECTRICAL DISCHARGES Irven H. Wilsey, Chicago, and John Evanston, Ill.

W. Meaker,

Application August 9, 1941, Serial No. 406,264

1'0 Claims. (Cl. 22S-62.5)

This invention relates to the perforation by electrical discharges of'sheet material such as Paper, composite fabric consisting of paper sheets and coating or filling strata, or other like fabrics, by means, for example of the apparatus disclosed in patent to Irven H. Wilsey, No. 1,790,452, January 27, 1931, or the apparatus disclosed in the application of John W. Meaker, Serial No. 358,041, filed September 23, 1940, in which dielectric sheet material is perforated by high voltage currents produced by a step-up transformer or by means of other electro-perforating apparatus. 'I'he sheet material thus perforated may be used for the manufacture of various articles such as bags, valve bags for example, or other containers such as open mouthed bags. The invention, however, is not to b considered as limited to the perforation of paper, or composite paper fabrics; nor to the production of bags; nor to the use of any particular electro-perforating apparatus.

A primary object of the invention is to provide certain means and procedures whereby the piercing of the fabric sheet or sheets by electrical discharges is facilitated -by associating with the sheet or sheets a substance, preferably in a pulverulent state and distributed with relative uniformity. upon, or within, or in case of the simultaneous perforation of several sheets, between said sheets, which substance is of such character, that is, of such relatively high electrical conductivity. as to facilltatethe penetration of the sheet or sheets by the electric arcs. This not only makes possible the electro-perforation of more or less highly resistant sheet material, that is material of high dielectric strength, without proportionate increase in voltages and current intensities, but also increases, under any circumstances, the number of perforations made over a given area in a given time and with a given equipment by minimizing the tendency of the discharges through perforations already made instead of piercing the fabric with new perforations. 'I'hat is, with the paper moving between a set of oppositely arranged electrodes there is always a tendency for the arcs to pass through already made perforations, due perhaps to the persistence of ionization, instead of valve bags, to make the bass waterproof. In such case the materials used for reducing the resistance of the dielectric may be distributed in the asphalt stratum.

'I'he preferred form of the invention is illustrated by way of example, in the accompanying drawing which is a vertical section through a sheet made of two layers of Doper with a layer of asphaltum therebetween and a vertical section through a layer of patent leather. The electric equipment is illustrated diagrammaticaily.

Looking at the figure, I represents a section through a sheet made up of two sheets of paper 2 and 3 with a layer of asphaltum 4 therebetween. Throughout the asphaltum are distributed particles of a substance of low dl-electric resistance, as shown at l. A pair of electrodes l, 9 are arranged one on each side of the sheet I. These are connected by conductors B and i with the high voltage side of transformer 2| which, in turn, is supplied with current by a motor generator set 20.

At Il is illustrated a sheet of patent leather or similar material. The fibrous hide is shown at Il and the hard glossy finished layer is shown lat i2. The latter has distributed throughout its thickness small particles of material with a low di-electric resistance. such as the particles shown at l.

At I8, I9 are electrodes connected -by conductors I5, I8, to the high voltage side of transformer 2 I.

In operating the device illustrated above, the sheet material would be moved along between the electrodes so as to perforate different parts of the sheet. The voltage and amperage utilized will be dependent upon the sheet material being acted upon and the character of the perforation desired. For commercial practice, rows of electrodes can be used and a relatively high voltage and low amperage isdesirable with a high cycle output. One form of the arrangement of electrodes is disclosed in copending application 393,134.

The invention may also be utilized in the electro-perforation, simultaneously, of a plurality of sheets by distributing the material between the sheets.

Suitable substances for the purpose are graphite. carbon black, aluminum, bronze or other metallic powders. in fact any pulverulent, granular, i'iaked or'otherwise finely divided material, the electrical resistance of which is relatively low.

Valve bags, or other bags having openings which closely nt the filling spouts of filling machines, in case the bags are used for packaging cement or other pulverulent material, if made of one or more envelopes composed of waterproof material, are difiicult to fill because of the imperviousness to air of the waterproofed paper which results in a trapping of air in the bag and necessitates, in actual practice, the use of larger bags for the same quantity of material than ii the bags had been made of more porous paper. The use of waterproofed paper involves, therefore, increased expense in two respects, i. e. a large quantity of paper and paper of more expensive character. The waterproofing of bags intended to contain cement, for instance, is desirable because the penetration of moisture into the bag sets and destroys the usefulness of a certain quantity of the cement. It is. therefore, particularly desirable to perforate bags made in whole or partly of waterproofed paper, both so as to allow the escape of air from the bags during the filling operation, as referred to above, and also to provide a breathing action when the bags are handled which minimizes bursting in case the bag A is dropped. This perforation may be effected by electrical discharges in which case the perforations will be made large enough to allow the passage of air but small enough so that no appreciable amount of liquid moisture can enter the bag. With asphalted paper the operation is difficult, requiring high voltages and current intensities; and it is also a relatively slow operation because of the tendency of the discharges, as adverted to above, to go through already made perforations instead of making direct paths by piercing the material with new perforations. B'y distributing graphite, carbon black or other pulverulent material through the asphaltum, the perforation of the paper-asphalt fabric (a fabric consisting, for example, of two sheets of paper with a stratum of asphaltum between them) is very much facilitated and the expense of the operation reduced. The use of carbon black in this connection is favored because of its low cost. The amount may be from 2% to '7% by weight of the asphaltum. A 2%'7% range is preferred as larger amounts of the material seem to increase the melting properties of the asphaltum. The invention, however, is not limited to the use of any particular amount of the material employed for reducing electrical resistance.

The invention may also be utilized in connection with the electro-perforation, simultaneously, of a plurality of sheets of paper, treated or untreated, that is, with the sheets superposed one upon or against the other. In such case the perforating operation is facilitated by distributingy between the sheets. a pulverulent substance of high electrical conductivity such as aluminum or bronze powder.

It would be possible to incorporate the pulverulent high conductivity substance in the paper itself; or in any manufactured fabric intended to be electrically perforated.

Considerable difficulty has been experienced in the electro-perforation of patent leathers, 'parculties have been overcome by adding to the lacquer about two per cent of carbon black based on the weight of the lacquer; or 6 per cent, by weight of bronze powder. The oxidized oil types of patent leather lacquers are more susceptible to electro-perforation than the pyroxylin type; but improved results are also obtained by the incorporation of pulverulent conducting material in such oxidized oil lacquers.

It is the intention to cover by patent all equivalents and modifications of the above described processes; and also the products of such processes.

We claim:

l. A bag comprising an envelope formed with a 'plurality of minute, electric arc pierced perforations, in the fabric of which envelope is dispersed a finely divided substance having a lower electrical resistance than the material constituting said fabric.

2. A bag, having a valved filling opening, comprising an envelope formed with a plurality of minute, electric arc pierced Ventilating perforations to allow the escape of air when the bag is filled, in the fabric of which envelope is dispersed a finely divided substance having a lower dielectric resistance than the material constituting said fabric.

3. A bag comprising a paper envelope treated with a stratum of waterproofing material in which is dispersed a finely divided substance having a lower dielectric resistance than the material constituting said stratum, said envelope being formed with a plurality of minute, electric arc pierced perforations.

4. A bag, having a valved filling opening, comprising a paper envelope treated with a stratum of waterproofing material in which is dispersed a nely divided substance having a lower electrical resistance than the material constituting said stratum, said envelope being formed with a plurality of minute, electric arc pierced Ventilating perforations to permit escape 0f air when the bag is being filled.

5. A bag comprising an envelope formed of asphaltum treated paper and provided with a plurality of electric arc pierced perforations; the asphaltum containing dispersed therein a finely divided substance having a lower dielectric resistance than the asphaltum.

6. A bag, having a valved filling opening, comprising an envelope formed of asphaltum treated paper and provided with a plurality of electric arc pierced Ventilating perforations; the asphaltum containing dispersed therein a finely divided substance having a lower electrical resistance than the asphaltum. A 7. Method of producing a multiplicity of pering through the asphaltum carbon black in a finely divided and dispersed state; and causing a plurality of electrical discharges to arc through said sheet material.

9. Method of producing a multiplicity of perforations by electric discharges in a sheet material having a substantially continuous coextensive coating characterized by a dielectric strength so high that electric discharges have a marked tendency to jump to nearby perforations rather than to pierce the sheet to form new perforations comprising uniformly incorporating in and distributing substantially throughout the area of said coating a substance, in finely divided and dispersed state, having lower dielectric resistance than that of said coating and facilitating electrical arc penetration therethrough, to provide paths of reduced resistance for electrical discharges, and causing a plurality of electrical discharges to arc through said sheet material and coating over said paths of reduced resistance, whereby the piercing of said sheet material with a relatively large number of perforations for a given area is facilitated.

10. Method of producing a multiplicity of perforations by electric discharges in a paper sheet material having a substantially continuous coextensive waterproof coating characterized by a dielectric strength so high that electric discharges have a marked tendency to jump to nearby perforations rather than to pierce the sheet to form new perforations comprising uniformly incorporating in and distributing substantially throughout the area of said coating a substance, in finely divided and dispersed state, having lower dielectric resistance than that of said coating and facilitating electrical arc penetration therethrough, to provide paths of reduced resistance for electrical discharges, and causing a plurality of electrical' discharges Ito arc through said sheet material and coating over said paths of reduced resistance, whereby the piercing of said sheet material with a relatively large number of perforations for a given area is facilitated.

IRVEN H. WILSEY. JOHN W. ll/IEAKER. 

